The present invention relates to a chip mounting device and a calibration method therein.
As is well known, in a chip mounting, relative to a chip retained by an upper head, a mounting part of a substrate (for example, a liquid crystal panel) retained by a lower substrate-retaining stage is precisely positioned, and at that state, the chip is mounted on the substrate by moving the head down. Therefore, prior to the mounting, for example, the positions of recognition marks for mounting (alignment marks) provided on the chip and the substrate are recognized by an appropriate recognition means such as a two-sight recognition means, and the relative position between the chip and the substrate is adjusted by controlling the position of the substrate-retaining stage so that a positional shift between both recognition marks disappear. At that time, the above-described recognition means is proceeded from its retraction position to its recognition position or retracted in the contrary direction.
However, in a period for carrying out mounting operations successively after such steps, since a dimensional variation may occur in respective parts of the device originating from a change of an environmental condition such as a rise of a temperature in an operation room, if the control for movement of the recognition means is carried out at an identical condition for a long period of time, an error may be generated in the positional recognition of the recognition marks for mounting. If an error is generated, a high-accuracy mounting may become difficult. Accordingly, in order to maintain a mounting accuracy of a xcexcm level, a calibration of the movement control system for the recognition means is carried out at an appropriate timing, as needed. With respect to such a calibration, various methods have been proposed.
For example, in a method disclosed in paragraphs [0036] to [0042], a mark table is attached to a Z table provided with a head (corresponding to a bonding tool) through a vertical movement device, and the mark table is moved to a position with the same level as that of a chip (corresponding to a semiconductor chip), which is retained by a head by vacuum suction, by driving the vertical movement device. Then, a recognition means (corresponding to a camera for a chip and a camera for a substrate) is moved below the mark table, and the recognition mark provided on the mark table (corresponding to a reference mark for calibration) is recognized. After the recognition means is retracted therefrom, the mark table is moved to a position with the same level as that of a substrate (corresponding to a circuit substrate) retained by the substrate-retaining stage (corresponding to a bonding stage) by driving the vertical movement device. The recognition means is moved to a position above the mark table, and the above-described recognition mark is recognized. Then, based on the control parameters obtained by both recognitions, the previous control parameters, which have been stored in the movement control system of the recognition means, are renewed for the following calibration.
In such a calibration method, however, at a position far away from the position for recognizing the recognition marks for mounting (alignment marks) provided on the chip and the substrate, respectively, a recognition mark for calibration different from the recognition marks for mounting is recognized. Therefore, the load (bending moment) acting on a movable table, which moves the recognition means, varies between when the recognition means is moved to a position for recognizing one mark among these marks (for example, the above-described recognition mark for calibration) and when the recognition means is moved to another position for recognizing the other mark (for example, the above-described recognition mark for mounting). Since the difference in deflection due to this variation may become an error in positional recognition of the recognition marks, a further high-accuracy calibration is obstructed.
Moreover, since the calibration is carried out at an appropriate timing based on experiences, the timing for the calibration is not always optimum, and therefore, the times of calibration may become many and unnecessary time may be accumulated.
Further, when a two-sight recognition means is employed, because its upper optical axis and lower optical axis are likely to be shifted, it is necessary to correct the shift, and because the correction parameters required for the correction can be determined experientially from the result of the measurement of the accuracy of the two-sight recognition means and the like but they are likely to be influenced by a change of season (a temperature change in environmental atmosphere) and the like, it is difficult to maintain the calibration accuracy constant. If the calibration accuracy is tried to be maintained constant, the time for the calibration may become long and the efficiency may reduce. Further, if the number of the times of calibration is reduced in order to shorten the time for calibration, it becomes difficult to maintain a desirable constant accuracy. Therefore, there have been insolvable problems conflicting with each other between the calibration time and the number oft he times of calibration.
Accordingly, an object of the present invention is to provide a chip mounting device and a calibration method therein wherein the number of the times of calibration can be decreased because each calibration can be carried out at an optimum timing, thereby performing each calibration efficiently, and a further high-accuracy calibration can be carried out without being influenced by the mechanical deformation of a movement control mechanism for a recognition means.
To achieve the above-described object, a chip mounting device according to the present invention comprises a first recognition mark on a chip-retainable head side and a second recognition mark on a substrate-retainable stage side, the first and second recognition marks being vertically apart from each other; a first recognition means for recognizing the first recognition mark and a second recognition means for recognizing the second recognition mark; a third recognition means for recognizing the first and second recognition marks concurrently when the first recognition mark is brought close to or into contact with the second recognition mark; and a temperature detection means for detecting a beyond-allowance temperature change to output a signal for initiating a calibration based on the concurrent recognition of the recognition marks.
A calibration method in a chip mounting device according to the present invention comprises the steps of recognizing a first recognition mark on a chip-retainable head side and a second recognition mark on a substrate-retainable stage side, the first and second recognition marks being vertically apart from each other; bringing the first recognition mark close to or into contact with the second recognition mark; concurrently recognizing the first and second recognition marks which have been brought close to or into contact with each other; and detecting a beyond-allowance temperature change to output a signal for initiating a calibration based on the concurrent recognition of the recognition marks.
Further, in the present invention, it is possible to concurrently recognize the first and second recognition marks without using a third recognition means. Namely, another calibration method in a chip mounting device according to the present invention comprises the steps of concurrently recognizing a first recognition mark on a chip-retainable head side and a second recognition mark on a substrate-retainable stage side, the first and second recognition marks being vertically apart from each other; and detecting a beyond-allowance temperature change to output a signal for initiating a calibration based on the concurrent recognition of the recognition marks.
In such chip mounting device and calibration method according to the present invention, the first and second recognition marks are concurrently recognized at a condition where they are brought close to or into contact with each other or at a condition where they are vertically apart from each other, the calibration is carried out based on the result of the concurrent recognition, and the actual calibration is performed only when a beyond-allowance temperature change is detected. A high-accuracy reading becomes possible by the concurrent recognition, and a calibration at an optimum timing can be carried out only when the calibration is required, by outputting a signal for initiating the calibration based on the detection of a beyond-allowance temperature change.
Therefore, according to the present invention, the calibration time can be shortened, a high-accuracy calibration can be carried out without being influenced by a mechanical deformation resulted by a moment caused from a positional difference between a position when the alignment of a substrate relative to a chip is carried out and a position when the calibration is carried out, and besides, the calibration can be carried out at an optimum timing and the number of the times of calibration can be reduced. As a result, the calibration can be carried out efficiently, and the accuracy of the calibration can be maintained constant, namely, the high accuracy can be maintained even when the temperature in the environmental atmosphere varies. Furthermore, because the number of the times of the calibration can be reduced while maintaining the high accuracy, the productivity can also be improved.